Estimating Underwater Light Regime under Spatially Heterogeneous Sea Ice in the Arctic

• Published in: Applied Sciences
• Main Authors: Philippe Massicotte, Guislain Bécu, Simon Lambert-Girard, Edouard Leymarie, Marcel Babin
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2018
• Subjects: apparent optical properties; 3D Monte Carlo numerical simulations; downward irradiance; upward radiance; sea ice heterogeneity; vertical attenuation coefficient; melt ponds; Technology; T; Engineering (General). Civil engineering (General); TA1-2040; Biology (General); QH301-705.5; Physics; QC1-999; Chemistry; QD1-999; Arctic; ice pack; Phytoplankton; Sea ice
• Online Access: https://doi.org/10.3390/app8122693; https://doaj.org/article/71a4fca5bf284d32ab88d882c6d31f2c

The vertical diffuse attenuation coefficient for downward plane irradiance ( <math display="inline"> <semantics> <msub> <mi>K</mi> <mi>d</mi> </msub> </semantics> </math> ) is an apparent optical property commonly used in primary production models to propagate incident solar radiation in the water column. In open water, estimating <math display="inline"> <semantics> <msub> <mi>K</mi> <mi>d</mi> </msub> </semantics> </math> is relatively straightforward when a vertical profile of measurements of downward irradiance, <math display="inline"> <semantics> <msub> <mi>E</mi> <mi>d</mi> </msub> </semantics> </math> , is available. In the Arctic, the ice pack is characterized by a complex mosaic composed of sea ice with snow, ridges, melt ponds, and leads. Due to the resulting spatially heterogeneous light field in the top meters of the water column, it is difficult to measure at single-point locations meaningful <math display="inline"> <semantics> <msub> <mi>K</mi> <mi>d</mi> </msub> </semantics> </math> values that allow predicting average irradiance at any depth. The main objective of this work is to propose a new method to estimate average irradiance over large spatially heterogeneous area as it would be seen by drifting phytoplankton. Using both in situ data and 3D Monte Carlo numerical simulations of radiative transfer, we show that (1) the large-area average vertical profile of downward irradiance, <math display="inline"> <semantics> <mrow> <mover> <msub> <mi>E</mi> <mi>d</mi> </msub> <mo>¯</mo> </mover> <mrow> <mo>(</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> , under heterogeneous sea ice cover can be represented by ...